Aerenchyma

Plants produce and utilize the gaseous hydrocarbon ethylene as a phytohormone throughout their life cycle. Ethylene is notoriously associated with fruit ripening and this aspect of its biology, along with its biosynthesis and mechanisms of signal transduction, has received a great deal of study. Many plants also employ ethylene signalling during instances of programmed cell death (PCD), including aerenchyma formation, epidermal PCD above emerging adventitious roots, senescence of petals, leaves, and reproductive structures, and endosperm death in developing cereal seeds. Ethylene-signalling during PCD is both spatially and temporally regulated, and is selective in that it induces PCD only in sensitized cells or tissues. This review examines instances of ethylene-regulated plant PCD, proposes a general model, and suggests avenues for future research that might improve our understanding of both PCD and ethylene signal transduction.

A well-developed aerenchyma is a major characteristic of aquatic plants. However, because such tissues are also found in wetland and terrestrial plants, it is not always possible to use their presence or absence to distinguish aquatic species. Whereas patterns of aerenchyma in roots have been studied in detail, those of the shoots have not. We collected and tested 110 species of various aquatic and wetland plants, including ferns (5), basal angiosperms (5), monocots (65), and eudicots (35). Three common and two rare types of aerenchyma were observed in their roots (three schizogeny and two lysigeny), plus five types of schizogeny in their shoots. We re-confirmed that, although a well-developed aerenchyma is more common in most organs of aquatic plants than in wetland plants, this presence cannot be used as strict evidence for the aquatic quality of vascular plants. Here, aerenchyma patterns were stable at the genus level, and the consistency of pattern was stronger in the roots than in the shoots. Furthermore, significant trends were verified in several higher taxa, and those consistencies of patterns partially coincided with their phylogeny.

To examine anatomical adaptations in a potential forage grass, Imperata cylindrica (L.) Raeuschel, a population was collected from the natural salt-affected soils of the Salt Range, Pakistan. Using a hydroponic system, the degree of salt tolerance in terms of structural modifications in the Salt Range ecotype was compared with that in an ecotype collected from a normal non-saline habitat of the Faisalabad region. The Salt Range ecotype was superior to the Faisalabad ecotype in biomass production under saline conditions. High salt tolerance of the Salt Range ecotype was associated with increased succulence in root and leaf (mainly midrib), formation of aerenchyma in leaf sheath, increased vascular bundle area, metaxylem area and phloem area, highly developed bulliform cells on leaves and increased sclerification in root and leaf. Furthermore, both stomatal density and stomatal area were considerably reduced under high salinities in the Salt Range ecotype.

The amphibious plant species of intermittent aquatic habitats thrive both submerged and emerged. In order to outline the adaptive characters of these two life forms photochemical efficiency of photosystem 2, leaf contents of chlorophyll (Chl) a and b, carotenoids (Car), anthocyanins (Ant), and UV-B absorbing compounds (UV-B abs), and root aerenchyma and arbuscular mycorrhizal (AM) colonisation were studied in Glyceria fluitans, Gratiola officinalis, Ranunculus lingua, Teucrium scordium, Sium latifolium, Sparganium emersum, and Veronica anagallis-aquatica. Water level fluctuations did not exert a severe effect on photon harvesting efficiency. Submerged specimens had higher contents of Car and Ant whereas higher contents of UV-B abs were found in emerged specimens indicating efficient protection against the harmful effects of solar radiation. Roots of all species studied had extensive aerenchyma and were colonised by AM fungi, which were significantly more abundant in emerged specimens. This is the first report on AM symbiosis in S. latifolium and S. emersum.

Summary Tree species from the Central Amazon inunda-tion areas are subjected to extreme flooding, with trees being partially submerged for up to 10 months. The rapidly advanc-ing floodwater table at the onset of the aquatic phase interrupts the inward diffusion of oxygen from the ...

Himatanthus sucuuba é uma espécie que coloniza as várzeas na Amazônia Central. O objetivo desse trabalho foi estudar as estratégias de adaptação da planta ao alagamento prolongado dessas áreas. Para tanto, foram acompanhados a germinação das sementes e o desenvolvimento das plântulas, simulando as condições naturais de campo (seca e alagamento). A germinação foi realizada em dois substratos: areia+serragem (não-alagado), e em água (alagado). Durante 120 dias, as plântulas geradas foram submetidas a três tratamentos: controle (irrigação diária), submersão parcial (sistema radicular) e submersão total. Foram analisadas as alterações na morfologia das plântulas, na anatomia das raízes e a atividade da enzima álcool desidrogenase (ADH), nos tempos: 0, 15, 30, 60, 90 e 120 dias. Foi constatado que a espécie apresenta elevada taxa de germinação e produção de plântulas, ambas acima de 80%, mesmo para sementes em água. Sob submersão parcial foram formadas lenticelas hipertrofiadas, raízes a...

A well-developed aerenchyma is a major characteristic of aquatic plants. However, because such tissues are also found in wetland and terrestrial plants, it is not always possible to use their presence or absence to distinguish aquatic species. Whereas patterns of aerenchyma in roots have been studied in detail, those of the shoots have not. We collected and tested 110 species of various aquatic and wetland plants, including ferns (5), basal angiosperms (5), monocots (65), and eudicots (35). Three common and two rare types of aerenchyma were observed in their roots (three schizogeny and two lysigeny), plus five types of schizogeny in their shoots. We re-confirmed that, although a well-developed aerenchyma is more common in most organs of aquatic plants than in wetland plants, this presence cannot be used as strict evidence for the aquatic quality of vascular plants. Here, aerenchyma patterns were stable at the genus level, and the consistency of pattern was stronger in the roots than in the shoots. Furthermore, significant trends were verified in several higher taxa, and those consistencies of patterns partially coincided with their phylogeny.

The stress of low oxygen concentrations in a waterlogged environment is minimized in some plants that produce aerenchyma, a tissue characterized by prominent intercellular spaces. It is produced by the predictable collapse of root cortex cells, indicating a programmed cell death (PCD) and facilitates gas diffusion between root and the aerial environment. The objective of this study was to characterize the cellular changes take place during aerenchyma formation in root of rice that accompany PCD. Scanning electron microscopy and transmission electron microscopy were used for cellular analysis of roots. Aerenchyma development was observed in both aerobic and flooded conditions. Structural changes in membranes and organelles were examined during development of root cortex cells to compare with previous examples of PCD. There was an initial collapse which started at a specific position in the mid cortex, indicating loss of turgor, and the cytoplasm became more electron dense. These cells were distinct in shape from those located towards the periphery. Mitochondria and endoplasmic reticulum appeared normal at this early stage though the tonoplast lost its integrity. Subsequently it underwent further degeneration while the plasmalemma retracted from the cell wall followed by death of neighboring cells followed a radial path. However, pycnosis of the nucleus, blebbing of plasma membrane and production of apoptotic bodies were not found which in turn indicated nonapoptotic PCD during aerenchyma formation in rice.